Optical proximity switch

Abstract

Optical proximity switch for detecting an object in a surveillance area, with a light transmitter (1), a lens (2), a photo receiver (3) and an evaluation unit (4) for generating a binary switching signal, wherein the light transmitter (1) is arranged on the underside of a printed circuit board (5) and the transmitted light can be emitted through a printed circuit board opening (6) into a lens tube (7), wherein the lens tube (7) has a pin (8) with a diaphragm (9) for beam limitation and is arranged in the printed circuit board opening (6) opposite the light transmitter (1).

Description

[0001] The invention relates to an optical proximity switch according to claim 1, in particular the design of the light transmitter and the optics.

[0002] Optical proximity switches are widely used in automation technology. They typically consist of an LED or laser diode as the light transmitter and a photodiode or phototransistor as the photoreceiver, along with an electronic circuit. The light transmitter, usually controlled by a high-frequency square-wave signal, generates a modulated light signal that is emitted into a monitored area, where it can be influenced by a trigger located there. The influence of the trigger on the light signal is detected by the photoreceiver and evaluated by the electronic circuit. If a threshold value is exceeded or undershot, an electronic switching stage is activated. Switching devices of this type are manufactured and distributed in a wide variety of designs, including by the applicant, for example, under the name OXxxxx.

[0003] The light signal can be evaluated in different ways. With through-beam sensors or energetic light sensors, the amplitude of the received light signal is evaluated. With retro-reflective sensors, it is the amplitude and degree of polarization. Furthermore, optical sensors are known in which the object distance is determined based on the time of flight of the light signal. In this case, the phase shifts between the emitted and received light signals are usually evaluated. Direct time-of-flight measurements are also possible. In many cases, the geometry of the emitted light beam determines the monitoring area. The reception area is usually chosen somewhat larger for technical reasons. Since the transmitting components have manufacturing tolerances and components from different manufacturers are used, the light beams are often limited by apertures.

[0004] Furthermore, it is necessary to ensure that the monitoring area, which, as mentioned above, is largely determined by the overlap of the projections of the transmitting and receiving components, is highly reproducible in series production. Therefore, the tolerance chain between the light-emitting and light-receiving surfaces and the optical components is kept as short as possible.

[0005] Another aspect is to keep optical crosstalk as low as possible in energetic sensors with adjacent transmitters and receivers. In practice, the power ratio should be at least 60 dB.

[0006] DE 100 32 796 A1 discloses an optical proximity switch with a light transmitter and a photoreceiver, along with the associated light channels and lenses. The light transmitter and photoreceiver are arranged side by side on the top of a circuit board. Crosstalk between the two light channels is additionally prevented by at least one elastic sealing element. Sealing is achieved by an oversize sealing contour relative to the side surfaces of the optoelectronic components.

[0007] The first disadvantage is the additional optical seal required. A further disadvantage, however, is that the unavoidable positional tolerances when soldering the light transmitter on the sensor affect the direction of the transmitted light beam. While this can be compensated for by a correspondingly larger reception range for large objects, it is problematic for small objects and can require adjustment effort when mounting the proximity switch.

[0008] DE 10 2010 025 734 A1 discloses a method for generating an input command for an optical sensor, in which an optical component of the sensor is used to trigger the command. In contrast to this general approach, the present invention focuses on a specific arrangement of the light transmitter and optics to reduce tolerance to manufacturing variations.

[0009] DE 20 2007 011 016 U1 describes an optical sensor in which the transmitter and / or receiver are mounted in a one-piece aperture tube to reduce stray light and achieve defined beam shaping. In contrast, the present invention addresses the problem of manufacturing tolerances and size by implementing a specific arrangement of the transmitter and optics on different sides of a circuit board.

[0010] The object of the invention is to provide a light transmitter with the associated transmission channel with low optical crosstalk that avoids these disadvantages. Furthermore, a homogeneous light spot with high energy density is to be created.

[0011] This object is achieved according to the invention by the features specified in claim 1. Advantageous embodiments of the invention are specified in the subclaims.

[0012] The key idea behind the invention is to use a single PCB hole for positioning both the light emitter and the lens tube. This reduces crosstalk from the emitter to the receiver by positioning them on different sides of the PCB, as well as shortening the tolerance chain for the position of the light emitter and the transmitting optics.

[0013] The invention is explained in more detail with reference to the drawings. They show: Fig. 1: An inventive light emitting unit for optical proximity switches, Fig. 2: The block diagram of an optical proximity switch according to the invention, Fig. 3: The light receiving unit for the light transmitting unit according to the invention.

[0014] Fig. Figure 1 shows the light emitting unit according to the invention. The light emitter 1 is a PointLED® from OSRAM. It can be mounted as an SMD component on the surface or on the underside of the circuit board 5. The LED is only 0.775 mm high and, in the illustrated through-hole mounting, protrudes approximately 0.5 mm into the circuit board opening 6.

[0015] The lens 2 is mounted on a lens tube 7, which has a pin 8 and a diaphragm 9. The pin 8 also protrudes 0.5 mm into the circuit board opening 6.

[0016] Depending on the focus position of the lens 2, the aperture 9 on the underside of the pin can act as a field stop or influence the aperture angle by blocking out marginal rays (stray light).

[0017] When aperture 9 is positioned at the focus of lens 2, a particularly homogeneous light spot is created. However, the maximum light intensity is achieved when imaging the LED chip. In this case, however, the bond pad also appears as a dark spot.

[0018] A significant advantage is seen in the short tolerance chain between the light transmitter 1 and the lens 2. The circuit board and thus also the positional deviations during the soldering process have virtually no influence on the beam direction.

[0019] In addition, the focal length of the lens 2 can be extended by the thickness of the circuit board 5, which is advantageous for small designs.

[0020] When using a light receiving unit according to Fig. 3, optical crosstalk is largely excluded because the light transmitter 1 and the photo receiver 3 are located on different sides of the circuit board 5.

[0021] Fig. Figure 2 shows a block diagram of the optical proximity switch according to the invention. It depicts an energetic sensor. The generator G belonging to the evaluation unit 4 generates a periodic square-wave signal, which is converted into a light signal by the light transmitter 1. The light is emitted through the circuit board opening 6 (not shown) and the aperture 9 into the lens tube 7 (also not shown), where the lens 2 generates a substantially parallel beam.

[0022] From a diffusely reflecting object, only one object point is shown here, the light is reflected according to the reflection incatrix of the object.

[0023] A portion of the reflected light is directed by the receiving lens onto the photoreceiver 3. The photoreceiver 3 represents a current source, which is advantageously converted into a voltage by a transimpedance amplifier. The resulting alternating voltage signal is fed to a rectifier, integrated, and evaluated with a trigger. If the trigger threshold is exceeded, the evaluation unit 4 outputs a binary switching signal.

[0024] Fig. Figure 3 shows the receiving unit. It corresponds to the known state of the art and therefore requires no further explanation. The advantage, as already mentioned, is the low optical crosstalk between the light transmitter 1 and the photo receiver 3 due to their arrangement on different sides of the circuit board 1.

[0025] The invention relates to an optical proximity switch for detecting an object in a surveillance area, comprising a light transmitter 1, a lens 2, a photoreceiver 3, and an evaluation unit 4 for generating a binary switching signal. The light transmitter 1 is arranged on the underside of a circuit board 5, and the transmitted light can be emitted through a circuit board opening 6 into a lens tube 7. The lens tube 7 has a pin 8 with a diaphragm 9 for beam limitation and is arranged in the circuit board opening 6 opposite the light transmitter 1.

[0026] In an advantageous embodiment, the photoreceiver 3 is arranged on the top side of the circuit board 1.

[0027] In a further embodiment, the aperture 9 is projected into the surveillance area by the lens 2 in order to produce a particularly homogeneous light spot. List of reference symbols 1 light transmitter 2 lenses 3 photo receivers 4 Evaluation unit 5 circuit board 6 PCB opening 7 Lens tube 8 cones 9 aperture G Generator

Claims

[1] Optical proximity switch for detecting an object in a surveillance area, with a light transmitter (1), a lens (2), a photo receiver (3) and an evaluation unit (4) for generating a binary switching signal, wherein the light transmitter (1) is arranged on the underside of a printed circuit board (5) and the transmitted light can be emitted through a printed circuit board opening (6) into a lens tube (7), wherein the lens tube (7) has a pin (8) with a diaphragm (9) for beam limitation and is arranged in the printed circuit board opening (6) opposite the light transmitter (1). [2] Optical proximity switch according to claim 1, characterized by that the photoreceiver (3) is arranged on the top side of the circuit board (1). [3] Optical proximity switch according to claim 1 or 2, characterized by that the aperture (9) is projected into the surveillance area by the lens (2).

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